Synthetic yarns,fabrics and processes for making the same



Oct. 14, 1969 J. 5. ROBERTSON 3,472,016

SYNTHETIC YARNS, FABRICS AND PROCESSES FOR MAKING THE SAME Filed July 11, 1966 2 Sheets-Sheet 1 DISTORTED WELT STITCHES INVENTOR. JACK SUTTON ROBERTSON 1969 J. s. ROBERTSON 3,472,016

SYNTHETIC YARNS, FABRICS AND PROCESSES FOR MAKING THE SAME Filed July 11, 1966 2 Sheets-Sheet 2 FIG. 2

ACCEPTABLE WELT STITCHES INVENTOR.

JACK SUTTON ROBERTSON United States Patent 3,472,016 SYNTHETIC YARNS, FABRICS AND PROCESSES FOR MAKING THE SAME Jack Sutton Robertson, West Asheville, N.C., assignor to American Enka Corporation, Enka, N.C., a corporation of Delaware Filed July 11, 1966, Ser. No. 564,234 Int. Cl. D02g 3/02 US. Cl. 57-140 8 Claims ABSTRACT OF THE DISCLOSURE An improved synthetic high modulus yarn product, e.g., nylon, having the ability to be knit into fabric with improved stitch clarity comprising a plurality of continuous synthetic filaments twisted together; the yarn having a tenacity ranging from about 6.0 to 8.0 grams per denier, elongation at break of from about 15 to 30%, a tensile moduli at elongation of from about 1.8 to 3.0 grams per denier, and a shrinkage in boilin water below about 9.0%.

The process for producing such synthetic yarns includes the steps of forming the yarn from continuous synthetic filaments, passing the yarn through a drawing zone heated to an elevated temperature below the melting point of the yarn, i.e., in the case of nylon, a temperature of from about 150 to 250 C., and simultaneously drawing the yarn in the zone at a draw ratio sufficiently high to obtain said physical properties, i.e., in the case of nylon, a draw ratio of from about 2.5:1 to 4.5 1.

This invention relates to synthetic yarns used for preparing knitted fabrics which exhibit improved stitch clarity and freedom from distortion. In particular, this invention relates to a process for producing high modulus nylon yarns having physical properties that make them especially useful as hosiery welt yarns in the knitting of hosiery, the resulting yarn products and the knitted fabrics made therefrom.

In the knitting of ladies nylon hosiery, special nylon yarns are often used to knit the felt or top of the hose and in some cases, the heel and toe portions. These yarns are usually knit in stitches which are considerably larger than those used to make the leg or foot portions of the hose. Large welt stitches have a great tendency to distort and to lose their shape resulting in the formation of defective sections designated as crowsfeet. The distortion may become so great as to make the hosiery welts commercially unacceptable.

In addition, it has also been found that the tendency of some nylon yarns to form knitted fabrics having an unacceptable distortion increases with aging of the drawn yarn.

Although the reasons for the distortion are not fully understood by the hosiery industry, many attempts have been made to reduce the distortion produced in nylon welt fabrics. Some of these attempts involve treating the yarn with gum, size, or special finishing agents before knitting it into a Welt in order to stabilize the larger stitches.

Also, it has been proposed to use partially drawn yarns, that is, yarns produced by lowering the draw ratio normally used, in an elfort to eliminate or reduce distortion of the larger welt stitches. Although this practice reduces the tenacity of the yarn, it often produces attractive welts. However, when these finished yarns and/ or the low modulus yarns are stored for a prolonged period, i.e., several Weeks or months, they have been found to produce crowsfeet and show excessive distortion when knitted into hosiery welts. Thus, in general, the hosiery industry has not eliminated and satisfactorily 3,472,016 Patented Oct. 14, 1969 solved the distortion problem which accompanies the use of nylon and the like synthetic yarns in the production of welts and other knitted pieces.

Advantageously, in accordance with this invention, improved synthetic yarns are produced which can be stored for prolonged periods after being drawn and packaged and still produce knitted fabrics substantially free from stitch distortion.

This invention contemplates a process for producing synthetic yarns having physical properties which enhance their ability to be knitted into fabrics of improved stitch clarity which comprises forming a yarn from continuous synthetic filaments, passing the yarn through a drawing zone heated to an elevated temperature below the melting point of the yarn and simultaneously drawing the yarn in the zone at a draw ratio sufficiently high to produce physical properties in the resulting yarn that permit fabrics knitted from the yarn to have improved stitch clarity.

More particularly, this invention is directed to a process for producing improved high modulus nylon welt yarns in which a multifilament nylon yarn is heated by passing it over a surface at a temperature of from about to 200 C. and is simultaneously drawn at a draw ratio in excess of 2.5 to 1 whereby the resulting yarn can be knitted into hosiery welts of improved stitch clarity.

Furthermore, this invention contemplates an improved synthetic high modulus yarn characterized by its ability to be knit into fabric having improved stitch clarity comprising a plurality of continuous synthetic filaments twisted together and having a tenacity ranging from about 6.0 to 8.0 grams per denier, an elongation at break of from 15 to 30% and tensile moduli at 5% elongation of from about 1.8 to 3.0 grams per denier.

This invention is also concerned with the knitted fabric made from the synthetic high modulus yarn which exhibits improved stitch clarity, has a finished distortion rating below about 4.0 and is especially useful for preparing hosiery welts.

In accordance with this invention, it has been found that synthetic yarns such as those formed from synthetic linear polycondensation products, especially the polyamide yarns, e.g., nylon 6, and the like, can be treated to produce yarn products suitable for the production of knitted fabrics having improved stitch clarity by drawing the yarns through a heated zone at a draw ratio higher than employed in the preparation of cold-drawn yarns. In general, the yarn is locally drawn over a pin or the like device while being passed over or adjacent to a heated surface for a sufficient period to heat it to a temperature from about 150 to about 200 C. and preferably to a temperature from about to about C. The surface used to heat the yarn may be provided by a heated draw pin, a hot plate positioned adjacent to a draw pin, or a like device which is heated by electrical resistance elements or by fluid heat exchange.

Advantageously, the yarn-to-surface contact of the traveling yarn with the heated surface may be varied considerably and still obtain the desired heat treatment. For example, the yarn-to-surface contact on a heated draw pin may vary from about 3 to about 15 inches either by changing the size of the draw pin or by altering the number of times the yarn is looped around the pin.

The yarn may be drawn by passing it to a feeding roller, around a draw pin, around a draw godet and an idler roll and finally to a pirn-forming device which may apply a twist to the yarn.

Oftentimes a pressure roller is operably associated with the feeding roller to prevent slippage of the yarn during drawing. Also, the yarn is normally laterally spaced on the positively driven godet bythe idler roll which has its axis slightly askew with that of the godet.

In this or other similar arrangements, the feeding roller and godet are rotated at different speeds to stretch the yarn in excess of 2.5 times its length. Generally, the yarn is drawn or stretched at ratios in the range of from about 2.5 :1 to 4.5 :1 and preferably from about 3.5:1 to 40:1 to produce a yarn product having the physical properties necessary for the purposes of this invention, e.g., high tenacity and high tensile modulus.

The yarn products of this invention can be used to prepare knitted fabrics substantially free from stitch distortion immediately after being put up. In addition, the yarns can be stored for prolonged periods, i.e., for several weeks to several months and then used to prepare knitted fabrics which are still substantially free from stitch distortion. For example, hosiery welts knitted from nylon yarns of this invention that were stored for more than eight months in a package have been found to have excellent appearance and show no quality deterioration with age.

The improved high modulus synthetic yarns of this invention possess a unique combination of physical properties that make them suitable for producing hosiery welts. In particular, it has been found that the yarn has tenacities that range from about 6.0 to 8.0 grams per denier and preferably from about 6.0 to about 7.5 grams per denier. Also, the tensile moduli of the yarn at 5% extension are at least 1.8 grams per denier and preferably extend from about 1.8 to 2.5 grams per denier. This high modulus level gives the yarn hand and appearance, e.g., silk-like, which is desired to produce welts having less distortion and improved stitch clarity.

In addition to the unique combination of high tenacity and high tensile modulus, the yarns of this invention also exhibit elongation at break of from about 15 to 25% and shrinkage in boiling water that is usually below about 9% and often below 7.

It will be appreciated that the yarns of this invention may have various denier sizes depending on their intended use. In general, the nylon yarns used in the preparation of hosiery welts will have a denier varying from about 30 to about 60 grams per 9000 meters and preferably from about 40 to 50 grams per 9000 meters. Moreover, the number of filaments in the yarn can vary from about 5 to about 20. Preferably from about 8 to about 15 filaments are employed to provide greater flexural stiffness to the yarn.

In accordance with this invention, the high modulus yarns are only twisted to a low degree, i.e., from about 0.25 to 1.0 turn per inch when packaged on a pirn-forrning device. It will be appreciated, however, that a higher degree of twist may be employed in some cases. Furthermore, although a Z twist may be employed, it has been found that the preferred yarns have an S twist of about 0.5 turns per inch.

The knitted fabrics produced in accordance with this invention are characterized by improved stitch clarity, i.e., retention of stich size and shape, and substantial freedom from distortion. Moreover, although the adverse effects caused by distortion are readily noticeable upon visual inspection of the fabric, particularly of hosiery welts, it is often ditficult to determine or judge the degree of distortion accurately. Accordingly, testing methods have been established to evaluate the knitted fabrics and to assign a numeral value to a fabric based on the amount of distortion found therein.

One such method provides a scale of finished distortion values that ranges from 0 through 10 in which 0 represents a fabric with perfect stitch clarity and 10 represents a fabric that has very bad distortion. Based on this scale, it has been found that hosiery welts with fininshed distortion values below 4.0 are readily acceptable by the hosiery industry; those with values of 4 to less 4 than 6 are just acceptable and those with values of 5 to 10 are considered commercially unacceptable.

The finished distortion values of the hose were accurately measured by counting the distorted areas on both the inside and outside of dyed and finished hosiery welts. If the distorted areas included more than two loops they were counted.

In order to more fully understand the significance of this method of evaluating distortion and its scale of finished distortion values, two finished welts are shown in the drawings in which:

FIGURE 1 shows a photomicrograph of a portion of a hosiery welt having unacceptable distortion and a finished distortion rating of 10 and;

FIGURE 2 shows a portion of a photomicrograph of an acceptable hosiery welt produced in accordance With this invention with a finished distortion rating of 0.

Inspection of the FIGURE 1 reveals that substantially all of the stitches in the welt are distorted and that the knitted courses are uneven. Also, there are highly distorted areas 2 and 4, and an extended distorted area 6 having many very defective stitches forming crowsfeet. The entire welt had an excess of 10 distorted areas.

In contrast, inspection of the hosiery Welt of the present invention shown in FIGURE 2 shows that it has even courses of stitches substantially free of any distortion and possesses excellent stitch clarity. Comparison of the two welts thus clearly points out that superior fabrics are obtainable by this invention.

It will be appreciated that the yarns and fabrics of this invention may be treated, i.e., coated, impregnated, or the like, with various synthetic and natural finishes, sizes or other processing aids that facilitate their knitability and serve to make them more suitable for their intended application.

The invention is further described in the following examples which are merely illustrative and not intended to be limitative of the scope of the invention.

Example I Undrawn yarn of nylon 6 having a denier of 40 and consisting of 13 filaments is drawn by passing over a feed roller, over two snubbing pins, over a hot plate having a 6 inch contact surface heated to C. and then 5 times around a draw roller at a drawing ratio of 3.76 to 1. Subsequently the yarn is taken from the draw roller onto a pirn at a rate of 1,233 feet per minute with a twist of 0.5 turn per inch in a counterclockwise direction, i.e., and S twist.

The resulting yarn is knit into hosiery welts and the welts are evaluated and found to have improved stitch clarity and substantial absence of distortion which is noted in welts knit from yarn that had been drawn in the conventional manner without heating in the drawing zone.

A test of the hot-drawn yarn shows that its physical properties include a tenacity of 6.1 grams per denier, an elongation at break of 24%, and a hot water shrinkage of 6.6%.

Example II TAB LE 1 Tensile Shrinkage Elong. mod. at in boiling Tenacity, atbreak, 5% el., water, per- Twist gJden. percent g.p.d. cent Hot Drawn 368 6.01 23.5 2. 28 7. 5 Cold Drawn %Z 5. 40 33.4 1.50 6.8

From the above data, it will be apparent that the hotdrawn yarn of this invention exhibits higher tenacity and higher tensile modulus than the conventional cold-drawn yarn.

Example HI Following the procedure outlined in Example I, a 40 denier nylon yarn consisting of 13 filaments is drawn over a 6 inch hot plate having a temperature of 190 C. After a short period, a portion of the yarn is knitted into hosiery welts that are characterized by improved stitch clarity.

Another portion of the yarn is allowed to remain put up in its package for approximately 10 months and then again knit into hosiery welts. Examination of the welts shows that they are still characterized by excellent stitch clarity and show no quality deterioration with age.

Example IV In this example, several samples of nylon yarn are drawn in a manner similar to that set forth in Example I with the exception that the yarn is passed over a 6 inch hot plate at a temperature of 185 C. located between a pair of draw pins and a draw godet. The draw ratios are selected to give tenacity of about 6.0 grams per denier, and an elongation of about 23% at break in the product yarns. As in Example I, all samples are prepared with an S twist using a pirn build-up. These product yarns having a denier of 40 and consisting of 8, 10, or 13 TABLE 2 Finished Hose Dis- Denierl- Typical Finish tortion til. Used 1 Value 1 /13 Stantex 1695- 3.0 40/13 do 3.0 2.0 3. 0 O 0 3.0 3. 0 4. 0 6.0

1 Finish manufactired by Standard Chemical Products, Inc. 2 0=Excellent stitch clarity; 10=very bad distortion.

Example V Additional samples of high modulus nylon yarn having a denier of 40 and consisting of 8 filaments are prepared using draw twisters equipped with feed roller, draw godet and a Dow-therm heated 60 mm. drawing pin located in the drawing zone. Also another yarn sample is prepared using the apparatus and procedure set forth in Example I in which a 6 inch hot plate is located in the drawing zone. Comparison of the physical properties of the resulting yarns (given in the following table) shows that various types of heating surfaces can be employed to obtain yarns having the required physical properties by using the hot-drawn process of this invention.

filaments are thein treated with a finish composition and knit into hosiery welts.

In addition, conventional cold-drawn nylon yarns having a denier of 40 consisting of 13 filaments are obtained and knit into hosiery welts. Comparison of the welts produced by the yarns of this invention (i.e., samples A through H) and that of the cold-drawn yarns (i.e., samples I and J) reveals that the yarns of this invention provide substantially less finished distortion than that of the conventional yarns. The results of these comparisons are given in further detail in the following table:

In this example, the effects of varying the number of filaments in the yarn, the surface contact and the temperature of the heated surface are further demonstrated by the production of several high modulus nylon yarn samples by drawing nylon yarns at a draw ratio of 3.76 to 1 over either a hot plate or draw pin onto a pirnforming device with a takeup rate of 1,233 feet per minute, and a spindle speed of 7500 rpm. which applies an S twist. The average physical properties of the resulting yarn samples are shown in the following table.

TABLE 4 Sample No.

Surface temp., C 195 195 195 180 180 185 185 Surface contact, in- 6 6 6 l1. 0 11.0 6. 5 6. 5 3 3 Den.lfil 40/8 40/10 40/13 40/8 40/8 40/8 40/8 40/8 40/8 Denier, drawnuu- 40. 2 40. 2 40.1 40.0 40.1 40. 0 40. 1 40.3 39. 9 Tenacity, g.p.d 6. 6. 2 6, l 6. 5 6. 1 6. 6 6. 2 6. 5 6. 4 Break el0ng., percent 26. 3 26. 5 23.9 24. 6 24. 6 24. 8 2A. 8 27. l 25. 5 Tensile modulus at 5% e10 2.1 2. 2 2. 1 2. 4 2. 3 2. 4 2. 2 2. 4 2. 3 Shrinkage in boiling water, percent- 6. 6 6. 5 6. 6 8. 0 8. 3 8. 3 8. 3 8. 4 7. 9

TABLE 5 Sample No.

passing the yarn through a drawing zone heated to a temperature of from about 150 to 250 C. and simultaneously drawing the yarn in said zone at a draw ratio of from about 2.5: 1 to 4.5 :1 whereby the welts knitted from the resulting yarn have improved stitch clarity.

5. The process of claim 4 in which said nylon filaments are made of nylon 6.

Surface temp., C

Surface contact, in- 6 Draw ratio 3.71 3.76 3.82 3.87 3.71

on] 40/8 40/8 40/8 40/8 40/ Denier, drawn 40.5 40.2 39.7 38.8 40.7 Tenacity, g.p.d 6.5 6 6 6.7 6 7 6.4 Break elong., percent 26.3 27 25.0 21 0 27.0 Tensile modulus at elong., g.p. 2.4 2 4 2.4 2 6 2.3 Shrinkage in boiling water, percent 7.6 7 8 7.8 7 7 8.5

What is claimed is:

1. An improved nylon high modulus Welt yarn characterized by its ability to be knit into hosiery welts having improved stitch clarity which comprises a plurality of continuous nylon filaments twisted together, said yarn containing from about 5 to 20 filaments and having a denier of from about 30 to about 60 grams per 9,000 meters, a tenacity ranging from about 6.0 to 8.0 grams per denier, elongation at break of from about to 30%, a tensile modulus at 5% elongation of from about 1.8 to 3.0 grams per denier and a shrinkage in boiling water below about 9.0%.

2. The yarn product of claim 1 in which said filaments are made of nylon 6.

3. A knitted hosiery welt having improved stitch clarity and being substantially free from distortion, said welt having been knit from high modulus nylon yarn and having a finished distortion rating below about 4.0 wherein said high modulus nylon yarn contains from 5 to filaments, and has a denier from about 30 to about 60 grams per 9,000 meters, a tenacity ranging from about 6.0 to 8.0 grams per denier and a tensile modulus at 5% elongation ranging from about 1.8 to 3.0 grams per denier.

4. A process for producing nylon welt yarns having physical properties which enhance their ability to be knitted into fabrics of improved stitch clarity which comprises forming a yarn from continuous nylon filaments, said yarn having a denier of from about 30 to about 60 grams per 9,000 meters and containing from 5 to 20 filaments,

6. The process of claim 4 which further comprises applying an S twist of from 0.25 to 1.0 turn per inch to said yarn.

7. The process of claim 4 which further comprises knitting a hosiery welt from said yarn, said welt having improved stitch clarity and substantial freedom from distortion.

8. The process of claim 7 in which said yarn is stored for prolonged periods before being knit into said welt.

References Cited MERVTN STEIN, Primary Examiner WERNER H. SCHROEDER, Assistant Examiner U.S. Cl. X.R. 57-157; 264--290 

